Pulse or digital communications – Systems using alternating or pulsating current – Angle modulation
Reexamination Certificate
1998-11-09
2002-01-29
Pham, Chi (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Angle modulation
C375S305000, C455S450000
Reexamination Certificate
active
06343104
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to a method for the modulation of a modulation carrier and to a mobile communication system.
Mobile communication systems as digital radio systems are known, for example, from M. Mouly, M.-B. Paulet, “The GSM System for Mobile Communications”, 1992. The transmission channels on a radio interface between two or more communications parties are variable in mobile communication systems and are subject to many influences, so that the quality of the transmission conditions can change fast.
For example, digital phase-shift keying modulations as described in M. Mouly, M.-B. Paulet, “The GSM System for Mobile Communications”, 1992, particularly pp. 249-259, are employed for modulation.
A digital phase-shift keying (PSK) is a modulation of a modulation carrier with amplitude and frequency kept constant, whereby every characteristic state of a discrete signal corresponds to a specific phase position of the modulation carrier. The transition from one phase position to the other can be a continuous or discontinuous modification. Further, MSK (minimum shift keying) modulation is also known, this being a specific form of CPFSK modulation (continuous phase frequency shift keying). CPFSK modulation is an FSK (frequency-shift keying) modulation given phase-continuous transition between the frequencies.
MSK modulation is a CPFSK modulation with a modulation index of that yields a compromise between noise resistance and bandwidth requirement given orthogonal signals and minimum frequency boost. MSK modulation, however, requires what is sometimes an unacceptably high transmission bandwidth or yields too low a data transmission rate, which can also often not be adequately improved by the smoothed version, for example the known GMSK modulation (Gaussian minimum shift keying).
It must be said that an incomplete bandwidth utilization of the transmission channel exists in mobile communication systems wherein the signals to be transmitted are modulated on a modulation carrier with such a modulation.
Given, for example, a comparison of digital mobile radiotelephone networks in a combined time-division multiple access (TDMA)/frequency-division multiple access (FDMA) as employed, for example, in the GSM (global system for mobile communication) mobile radiotelephone system to a code-division multiple access method (CDMA), a better bandwidth utilization of the CDMA networks is often cited, whereby what is understood by bandwidth utilization is the number of channels per available bandwidth and radio cell. In practice, however, a high bandwidth utilization is difficult to realize in CDMA networks, among other things because of the required synchronization. U.S. Pat. No. 4,495,619 discloses a modulation method for a satellite communication system wherein the desired number of steps are selectable.
SUMMARY OF THE INVENTION
An object of the invention is to specify measures for increasing the bandwidth utilization in a mobile communication system.
In general terms the present invention is a method for the modulation of a modulation carrier, whereby a modulation form that is variable in view of its number of steps is provided for a digital transmission channel and the number of steps of the modulation is adaptively matched during operation to the respectively existing transmission conditions. A set of the steps in a modulation with a specific number of steps is a sub-set of the set of steps with the next-higher number of steps.
A training sequence that does not change in the adaptation of the number of steps is transmitted in the digital transmission channel.
A largely constant error probability is achieved by the adaptation of the number of steps in this transmission channel.
A time-division multiplex time slot is respectively to a plurality of transmission channels. The adaptation of the number of steps of the modulation carrier of a transmission channel matched to the transmission conditions are linked with a modification of transmission time resources of this transmission channel that are made use of such that the data transmission rate of this transmission channel remains essentially constant.
The allocation of time slots to transmission channels matched to the transmission conditions is based on a high plurality of transmission channels.
The form of modulation variable in view of its number of steps is determined such that a set of modulated modulation carriers of all possible signals (bit sequences) is a sub-set of a set with the next higher number of steps given modulation with a specific number of steps.
The present invention is also a mobile communication system for signal transmission over a radio interface between a base station and a mobile station that respectively has at least a modulator and a demodulator upon employment of a multi-step modulation of a modulation carrier. A means for the determination of the transmission conditions are provided in the base station and/or the mobile station. A form of modulation variable in view of its number of steps is provided by the modulator and the demodulator. The modulator and the demodulator adaptively match the number of steps of the modulation in the respective digital transmission channel on the radio interface to the transmission conditions respectively present during operation. The modulator is fashioned such that a set of the steps in a modulation with a specific number of steps is a sub-set of the set of steps with the next-higher number of steps.
Advantageous developments of the present invention are as follows.
With the modification of the number of steps in the respective transmission channel, a largely constant error probability that can be identified by the means for the determination of the transmission conditions is achieved by the modulator and by the demodulator.
The radio interface is fashioned according to a time-division multiplex method and/or a combined time-division multiplex/frequency-division multiplex method.
The adaptation of the number of steps of the modulation carrier of a transmission channel matched to the transmission conditions by the modulator and by the demodulator are linked with a modification of transmission time resources of this transmission channel that are made use of such that the data transmission rate of this transmission channel remains essentially constant.
The allocation of time slots to transmission channels matched to the transmission conditions is based on a high plurality of transmission channels.
The form of modulation variable in view of its number of steps is determined such that the spectral width of the transmission channel is not enlarged given modification of the number of steps.
A modification of the number of steps of the modulation of the respective digital transmission channel is linked such with a modification of the transmission power and is monitored by the means for determining the transmission conditions such that an adequate signal-to-noise ratio given a high number of steps can be achieved by a higher transmission power.
The system is a GSM or GSM-like mobile radiotelephone system. For improving the bandwidth utilization, the transmission quality is monitored at the reception side given a transmission between a mobile station and a base station. Given determination of an adequate transmission quality, a switch is made from the use of a “full rate” traffic channel to a “burst half rate” traffic channel wherein, analogous to a “half rate” traffic channel, one-half the time slots is used on average, and the payload data correspond to those of a “full rate” traffic channel due to the provision of a 4-step phase modulation instead of a 2-step phase modulation.
The 4-step phase modulation in the “burst half rate” traffic channel is designed such that the occupied bandwidth per carrier frequency is not changed compared to the known two-step GMSK modulation.
Proceeding from a “half rate” transmission, for example given improved voice encoding, and analogous switch given good transmission quality is made from a “half rate” transmission channel
Pham Chi
Phu Phuong
Siemens Aktiengesellschaft
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